Implantable medical leads are used in a variety of applications to conduct energy (e.g., electrical, photonic, etc.) between energy sources and various portions of the body. Diagnostic leads are implanted to measure physiological parameters over time, for example blood pressure, or collect and transmit physiological data such as nerve impulses and cardiac rhythm data. Stimulation leads discretely deliver energy to targeted tissues. Neurological stimulation leads are used to block pain, for example. Cardiac stimulation leads are used to deliver low or high voltage electrical energy to pace or defibrillate the heart.
Transvenous defibrillator leads are used for the correction of ventricular or atrial bradycardia, tachycardia and/or fibrillation. Leads of this type are intravenously positioned, and are used to provide a variety of diagnostic, pacing and defibrillation functions. More than one electrode may be provided if it is desired to provide electrodes for defibrillation and for pacing and/or sensing. Typical cardiac leads are positioned into the right atrium and/or the right ventricle. More recently developed leads are positioned into the coronary veins of the left side of the heart for use with cardiac resynchronization therapy (CRT).
Conventional transvenous defibrillator leads use a stranded wire to conduct the electrical energy from the connector at the proximal end of the lead to a coiled defibrillation electrode near the distal end. A discrete connector or junction is generally used between the conductor and the electrode. The junction may be formed by a connector component, a crimp joint, a weld, or combinations of these. Medical leads with discrete connectors may suffer from decreased reliability due to connector interfaces serving as points of failure. Connectors also tend to increase the diameter of leads, at least in the region of the connector. This may lead to increased tissue attachment in these regions and commensurate difficulty in lead extraction (sometimes necessary in cases of infection, dislodgement or lead failure).
The electrode surface of an implantable lead is typically exposed, allowing it to contact or be in close proximity to the desired surface of the tissues or surrounding fluids. Such exposed electrodes have a fundamental disadvantage with tissue ingrowth. The ingrowth and anchoring of tissue into the exposed coil makes the lead difficult to extract and may also adversely affect electrical performance of the lead. Various electrode coverings have been suggested to eliminate or minimize tissue attachment to the electrode. Defibrillation electrodes provided with coverings of porous polymeric materials including polyurethane and polytetrafluoroethylene (hereinafter PTFE) have been described, wherein the penetration of bodily fluids permits electrical conduction through the porous polymer even though the covering itself may be electrically non-conductive. Various electrically conductive coverings such as porous polymeric materials having void spaces partially filled with conductive materials (e.g., carbon) have also been described. These porous coverings may be treated to improve wettability and conductivity.
It has generally been desired to manufacture leads with the smallest possible diameter while providing sufficient electrode area. Other sought after attributes may include isodiametricity, flexibility, flex life, fatigue resistance, abrasion resistance, corrosion resistance, tensile strength, and minimal tissue ingrowth, all of which contribute to good long-term reliability and extractability with minimal risk of trauma.